Why did Paul Keim, chair of the National Science Advisory Board for Biosecurity (NSABB) say “I can’t think of another pathogenic organism that is as scary as this one”. What lead Donald McNeil, writing about H5N1 in the New York Times, to conclude that “In its natural form, it is known to have infected only about 600 people since its discovery in 1997, but it killed more than half of them.”